The current wave of three-dimensional (3D) films is gaining popularity, which is made possible by the ease of use of digital technology and especially 3D digital cinema projection systems. However, the availability of new 3D digital cinema projection systems has been inadequate to keep pace with demand the demand for the new systems. Moreover, theater owners are finding that the changeover to the 3D digital cinema projection systems is very expensive business proposition. As a result, there is currently a move to satisfy the demand for 3D films without the use of digital technology by deploying stereoscopic film prints for presentation using a stereoscopic 3D projector.
Earlier 3D film systems were and continue to be considerably less expensive than the digital cinema approach. However, the earlier film systems experienced difficulties relating to configuration, brightness, and discoloration of the picture, among others. If improvements could be found in a film-based 3D presentation system for the image separation, color, and brightness of the 3D images and if those potential solutions could compete with, if not exceed, the related characteristics in the digital cinema presentations, then it would be possible to present a 3D film based product with sufficiently high quality to attract audiences to the same degree that digital cinema 3D attract audiences today.
However, in these prior film-based 3D systems, movement of the lens or projector lamp or other illuminator components can result in a change in the alignment of the system. When the system alignment is changed, a gross differential brightness of the projected right- and left-eye images occurs along with vertical and horizontal alignment errors. These alignment or brightness balance errors, depending on their respective degree, can result in severe eye fatigue and a potentially unpleasant viewing experience for the audience.
Back in the 1980's, a wave of 3D films were shown in the US and elsewhere, making use of a lens and filter described by Condon in U.S. Pat. No. 4,464,028, which is expressly incorporated by reference in its entirety. Horizontal and vertical alignment were achieved with varying degrees of success by projecting a film having substantially the same image as each image of the stereoscopic pair, and using the projected image as a visual aid to adjust the system for proper alignment. But little, if anything, was done to adjust and correct the differential brightness due to misalignment because this condition is difficult to view from the projection booth due to a hot spot formed on a high-gain silver screen.
As a result, the known prior methods and apparatus appear to lack any suitable solutions for overcoming the problems related to orientation, convergence and brightness balance in 3D film-based projection systems.